The Responses of Ammonia-Oxidizing Microorganisms to Different Environmental Factors Determine Their Elevational Distribution and Assembly Patterns

The assembly mechanisms shaping the elevational patterns of diversity and community structure in ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) are not well understood. We investigated the diversities, co-occurrence network patterns, key drivers, and potential activities of AOA and AOB communities along a large altitudinal gradient. The α-diversity of the AOA communities exhibited a monotonically decreasing pattern with increasing elevation, whereas a sinusoidal pattern was observed for the AOB communities. The mean annual temperature was the single factor that most strongly influenced the α-diversity of the AOA communities; however, the interactions of plant richness, soil conductivity, and total nitrogen made comparable contributions to the α-diversity of the AOB communities. Moreover, the β-diversities of the AOA and AOB communities were divided into two distinct clusters by elevation, i.e., low- (1800-2600 m) and high-altitude (2800-4100 m) sections. These patterns were attributed mainly to the soil pH, followed by variations in plant richness along the altitudinal gradient. In addition, the AOB communities were more important to the soil nitrification potential in the low-altitude section, whereas the AOA communities contributed more to the soil nitrification potential in the high-altitude section. Overall, this study revealed the key factors shaping the elevational patterns of ammonia-oxidizing communities and might predict the consequences of changes in ammonia-oxidizing communities.